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authorColin Cross <ccross@android.com>2013-05-06 23:50:11 +0000
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2013-05-12 14:16:22 +0200
commit613f5d13b569859171f0896fbc73ee0bfa811fda (patch)
tree92f3f25db1fe1063624cc0ef69506d2f38a1988a /kernel/freezer.c
parent18ad0c6297df1d671ecea83b608cd9e432642a05 (diff)
downloadlinux-sh-613f5d13b569859171f0896fbc73ee0bfa811fda.tar.gz
freezer: skip waking up tasks with PF_FREEZER_SKIP set
Android goes through suspend/resume very often (every few seconds when on a busy wifi network with the screen off), and a significant portion of the energy used to go in and out of suspend is spent in the freezer. If a task has called freezer_do_not_count(), don't bother waking it up. If it happens to wake up later it will call freezer_count() and immediately enter the refrigerator. Combined with patches to convert freezable helpers to use freezer_do_not_count() and convert common sites where idle userspace tasks are blocked to use the freezable helpers, this reduces the time and energy required to suspend and resume. Acked-by: Tejun Heo <tj@kernel.org> Acked-by: Pavel Machek <pavel@ucw.cz> Signed-off-by: Colin Cross <ccross@android.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'kernel/freezer.c')
-rw-r--r--kernel/freezer.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/kernel/freezer.c b/kernel/freezer.c
index c38893b0efba..8b2afc1c9df0 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -110,6 +110,18 @@ bool freeze_task(struct task_struct *p)
{
unsigned long flags;
+ /*
+ * This check can race with freezer_do_not_count, but worst case that
+ * will result in an extra wakeup being sent to the task. It does not
+ * race with freezer_count(), the barriers in freezer_count() and
+ * freezer_should_skip() ensure that either freezer_count() sees
+ * freezing == true in try_to_freeze() and freezes, or
+ * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
+ * normally.
+ */
+ if (freezer_should_skip(p))
+ return false;
+
spin_lock_irqsave(&freezer_lock, flags);
if (!freezing(p) || frozen(p)) {
spin_unlock_irqrestore(&freezer_lock, flags);